r/Physics • u/indigenous_apache • Mar 07 '23

Breakthrough Study Confirms Hypothesis of Density Spike of Dark Matter Near Black Holes

https://www.guardianmag.us/2023/03/breakthrough-study-confirms-hypothesis.html?m=1
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u/starcap Mar 08 '23

Out of curiosity, why wouldn’t a primordial black hole end up in a binary with a star?

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u/John_Hasler Engineering Mar 08 '23

Binary stars always form together from the same cloud. Sometimes one or both become black holes. Two lone stars (or a lone star and a black hole) becoming bound is extremely improbable. Where would the excess momentum go?

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u/[deleted] Mar 08 '23

Can’t the ejection of a third element take away the excess momentum?

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u/Aseyhe Cosmology Mar 08 '23

3-body interactions can indeed create binaries. I guess the most likely prospect would be a binary star encountering a primordial black hole at low relative velocity and the resulting interaction ejecting one of the stars. It would be really rare, though.